Multi-coil vertical tube heater



Oct. 21,1958

Filed April 10, 1957 T. B. LEECH ET AL 2,856,903

MULTI-COIL VERTICAL TUBE HEATER 2 Sheets-Sheet l INVENTORS 3/ fi/oM/ls [55% Arrow/5);!

Oct. 21, 1958 T. B, LEEcH ETAL 2,856,903

MULTI-COIL VERTICAL TUBE HEATER Filed April m 1957 2 Sheets-Sheet 2 Z0 '7 INVENTORS f/m/ms- 5 55017 y Joy/y 51 144415 Arm/2mm.

United States Patent 2,856,903 MULTI-COIL VERTICAL TUBE HEATER Thomas B. Leech, Scarsdale, and John S. Wallis, New

York, N. Y., assignors to Petro-Chem Process Company, Incorporated, New York, N. Y., a corporation of Delaware Application April 10, 1951, Serial No. 651,890 2 Claims. Cl. 122-356) This invention relates to new and useful improvements in furnaces and heaters of the vertical type, such as that shown in U. S. patent to I. S. Wallis et al., No. 2,333,077, granted October 26, 1943.

One object of the invention is to provide a unitary heater or furnace which shall retain the advantages of the vertical tube radiant heaters, as exemplified by the above patent, but which shall at the same time incorporate a primary heating coil and one or more independentheating coils whereby the structure is particularly adapted for use in providing the entire heating requirements of catalytic .reformingprocesses which are now generally employed for upgrading petroleum fractions boiling in'the gasoline range.

Several different processes for catalytically reforming naphtha toproduce high octane gasoline and in which extraneous hydrogen or recycled hydrogen is supplied to the process are described and illustrated by flow diagrams,

in the Oil and Gas Journal of March 17, 1952. These processes aim to maintain such conditions of temperature, pressure and time as are favorable to desired reactions, such as dehydrogenation and dehydroaromatization, and they aim to avoid operating conditions which favor undesirable reactions, such as hydrocracking and thermal cracking. 1

The aforesaid desired reactions are endothermic and absorb very large quantities of heat and to avoid using high temperatures, which are undesirable, it has hitherto been foun'd desirable to utilize several heaters, one raising the temperature of the naphtha charge, another for heating the recycled gas and in some of the processes the main reactor containing the catalyst is divided into sections and the charge is first heated in one of the reactors and is then passed through an intermediate heater to restore its temperature before going to the second. Another intermediate heater is used in some cases where three (3) reactors are employed.

Provision of a number of different furnaces'or heaters involves undesirable expense and the heater of our invention is a unitary heater having two more independent coils in which desired temperature conditions can be maintained, while at the same time the total heat quantity supplied to all the heaters is large and entirely adequate to supply the needs of such processes as above referred to.

The preferred embodiment of our invention is illustrated in the accompanying drawings and hereinafter described;

v Figql is a sectional elevation of a tall cylindrical heater broken away to economize vertical space on the drawing so that important features of the heater are shown on a larger scale;

Fig. 2 is a sectional plan view taken on the line 22 of Fig. 1; and

Fig. 3 is a sectional plan view taken on the line 3-3 of Fig. 1.

Referring to the drawings, the heater illustrated comprises a large cylindrical furnace chamber 11) having a steel shell 11, which may be welded in the field by a Patented Oct. 21, 1958 ice steel fabricator, a lining 12 of monoblock insulation or the like and a firebrick lining 13. The furnace has a bottom plate 14 having 4 burners 15 mounted near the cen-' which the small burners 16 discharge.

The furnace chamber 10 is supported on structural steel beams or columns Zll which extend below thebottom of the furnace and constitute supporting legs 21 as shown in Fig. 1. Thus the furnace floor is above the foundation 22 so as to enable operators to enter the space and adjust the burners or otherwise service the furnace. The

steel cylinder 23 of smaller diameter than the cylinder 11 is concentrically mounted at the top of the furnace chamber and is supported by beams 24, which may be welded to and form extensions of the columns 20.

The main chamber 10 has an annular steel top 25,

belowwhich is an annular refractory arch 26. The cylindricalshell 23 is also provided with suitable insulation and brick lining corresponding to that provided in the main cylinder.

A cylindricalbaffle 30, which is closed at the top by a plate 31 having a manhole cover 32, is supported by bolts 33 from the stack superstructure 34. This structure is cylindrical in form and is smaller in diameter than the shell 23 to which it is connected by an annular ledge plate .35. The superstructure is supported by beams 36 which extend upwardly from the beams 24 and terminate in beams 37, to which the stack structure 34 may be welded. The stack is designated 38. The furnace has heat exchange elements which contain the different fluids to be heated and these elements comprise a main heating coil- 40 composed of vertical tubes interconnected in series at their ends, constituting a circular bank close to the wall of the cylindrical chamber 16, but extending downwardly from the top for a distance of about two-thirds or three-quarters of the entire length of the furnace chamber 10. This tubular heat exchange element 40 is supported from the annular top plate 25 by U-bolts 41 and the tube bank of this element is held in a concentric position with reference to the entire wall of the chamber 10 by spacing supports 42. A second heat exchange element 43 is made up of a helix constituting a tube bank having the form of a segment of a cylinder and provided with an inlet connection 44 and an outlet connection 45, as shown in Figs. 1 and 3. This helical coil extends circumferentially about two-thirds of the way around cylindrical chamber 10 and is close to the inner wall of said chamber.

-A third heat exchange element 50 is similar to the element 43 and has an inlet 51 and an outlet 52 but its helix, which also constitutes a tube bank having the form of a segment of a cylinder, extends approximately onethird of the way around the cylindrical shell and together with the element 43 largely follows the wall of the chamber 10 but only extends axially for about one-quarter or one-third ofthe length of the chamber 10 so that-the coils are spaced from and do not-interfere with :the vertic'al tubes 40. I I The bafiie 18 as shown extends axially to about twothirds of the height of the tube cylinder formed by the elements 4.3 and 50. The tubular heat exchange elements 43 and 50 are supported by the furn'ace at the bottom, each tube of the coil being separated by spacers 53.

The intense flame from the 4 large burners 15 is discharged, together with the hot gases, axially upward and supplies heat by radiation to the upper inlet portions of 3 the elements 43 and 50 and to the vertical tubes 4d of the primary heat exchange element.

The furnace chamber is very tall and depending from the top is a conical bafile 56 so that when the hot gases have given up a substantial quantity of heat by radiation, they are diverted around the upper endsof the tubes 40 and thence flow inwardly and upwardly through a relatively annular narrow chamber 57, which is formed by the'inner wall of the chamber 23 and the outer wall of the batlle 30.

'Mounted in this annular space is a vertical tube convection heater element 60 which is made up of fin tubes so that a large percentage of the remaining heat is ex tracted from the gases which flow through the annular passage around these tubes. The spent gases are discharged into the stack 38. The heat exchange element ,60'has an inlet Connection 61 and an outlet connection 62, as shown in Fig. 1. The element 60 is supported on the annular ledge 35. Frusto conical covers protect the upper ends of the vertical tube heat exchange element 40 and of the heat exchange element 60, the larger one over the element 46 is designated 65 and the smaller one over the element 69 is designated 66.

The tubular heat exchange element 60 is intended primarily as a preheating element when the furnace is utilized, as herein explained, for the purpose of supplying heat to a catalytic reforming process and the charge enters the inlet 61 and will be discharged from outlet 62. Suitable piping, not shown, may connect the same stream, the temperature of which is already increased to approximately 360 F. into the inlet 70 of the primary vertical tube heating element 40. The charge is then discharged through the outlet 71 at a relatively high temperature.

In 71 the hot naphtha is led into the primary reactor of the system and due to the endothermic reaction taking place, it is discharged therefrom at substantially reduced temperature and is then boosted by being passed through the heat exchange element 43 entering the inlet 44 and being discharged through the outlet 45. From thence the product at this intermediate stage with its temperature again elevated to the desired level is passed into a second reactor.

If the system has a still further reactor the product may be led from the second reactor through the heating element 50 and will enter at the inlet 51 and be discharged at the outlet 52. It the process involves the heating of the extraneous hydrogen or recycled hydro-gen, this operation may be accomplished in one of the heating elements.

The heat exchange elements 43 and 50 are supplied with heat from the circularly arranged burners 16 which discharge axially in the annular space between the bafile 1S and the inner wall of the furnace chamber 19. The hot gases from these burners join the hot gases from the main burners and continue upwardly inside of the circular bank of the main heater.

The temperature control for each of the several heaters may be maintained as desired by regulating the burners and 16. For example, it is usually desirable to boost the temperature of the fluid stream by the application of larger heat quantity in element 43 than is necessary in element 50.

The tall vertical cylindrical type of heater has well known advantages in economy of construction, and by our present invention these economies are retained while primary and one or more secondary heating elements are embodied in a unitary structure composed of a single cylindrical furnace.

While we have shown and described one embodiment of ourinvention .as applied to. a-catalytic.reformingunit,

it is equally applicable to other processes where multicoils with separate heat control are desirable. For example, this arrangement may be used for an atmosphericvacuum distillation unit where one coil would be used for the atmospheric stage, a second coil for the vacuum stage and a third coil for superheating steam required in the process. It 'is also applicable for certain types of distillation units Where one .coil would be utilized for heating the charge, a second coil for the reboiler stage and a third coil for an even different service.

We desire that modifications which do not depart from the spirit of the invention .be included and thatonly such limitations be imposed as are indicated in the appended claims.

What we claim is:

1. A unitary furnace comprising a tall cylinder forming a combustion chamber, 'a primary vertical heat exchange element composed of a circular bank of tubes located near the wall of the chamber and extending from the top of the chamber approximately two-thirds of the way down, one or more secondary heat exchange elements positioned in the furnace chamber below the primary heat exchange element and concentric'therewith, a baffle extending upwardly from the bottom of the furnace chamber for about two-thirds the height of-the secondary element or elements, burners located within the bafile and discharging axially through the baflle into the furnace chamber, and additional independently controlled burners between thebafile and the secondary element or elements discharging axially outside of the battle and inside of the tube bank or banks constituting the secondary heat exchange element or elements.

2. A unitary furnace having a tall cylindrical shell forming a furnace chamber with-its axis vertical, a plurality of heat exchange elements, one having vertical tubes interconnected to form a'cylindrical bank within the upper portion of the chamber and adapted to act as a primary heater in a catalytic gasoline reforming system, and two additional heat exchange elements adapted to act as intermediatesecondary reheaters having circumferentially extending tubes, the tubes of each element being interconnected to form a segmental cylindrical bank, one of which is a larger arcuate coil and the other a smaller arcuate coil, and together forming'a complete cylinder of tube banks within the lower portion of the chamber, a hollow cylindrical bafile of intermediate size extending upwardly from the bottom of the chamber and'coaxial with and extending within said'cylinder of tube banks to about two thirds of theheight o'f'saidtube banks, and forming a central fire pot and an outer annular fire chamber, and independently controlled burners discharging axially upward within the central fire pot and additional burners independently controllable, circumferentially distributed and discharging axially into the annular fire chamber, whereby the heat applied to the larger and the smaller arcuate coils may be varied relative to each other.

References Cited in the file of this patent UNITED STATES PATENTS 

